Over the past three years we have gained considerable experience with the percutaneous catheterization of the adrenal veins in human subjects. In our experience this procedure has been extremely well tolerated by the patients and has permitted sampling of adrenal venous blood at very frequent intervals. We plan to use this approach to delineate in detail the secretory patterns of cortisol and aldosterone and the newly described inverse relation between the secretion of these two steroids. Comparison of the concentration of these two steroids in the adrenal veins and in the peripheral plasma will also permit to establish for the first time a mathematical correlation between these two variables. The adrenal secretion of androgens and the factors controlling it will be studied later in the project.